1. Field of the Invention
This invention relates generally to feed cable systems for drilling machines.
2. Description of the Related Art
There are many different types of drilling machines for drilling through a formation. Some of these drilling machines are mobile and others are stationary. Some examples of mobile and stationary drilling machines are disclosed in U.S. Pat. Nos. 3,245,180, 3,692,123, 3,708,024, 3,778,940, 3,815,690, 3,833,072, 3,905,168, 3,968,845, 3,992,831, 4,020,909, 4,170,340, 4,478,291, 4,595,065, 5,988,299, 6,672,410, 6,675,915, 7,325,634, 7,347,285 and 7,413,036, as well as U.S. Patent Application No. 2003056989 and International Application No. PCT/NO96/00310. Some drilling machines, such as the one disclosed in U.S. Pat. No. 4,295,758, are designed to float and are useful for ocean drilling. The contents of these cited U.S. Patents are incorporated by reference as though fully set forth herein.
A typical mobile drilling machine includes a vehicle and tower, wherein the tower carries a rotary head and drill string. The rotary head is coupled with the tower using a feed cable system, wherein the feed cable system allows the rotary head to move between raised and lowered positions. In operation, the drill string is driven into the formation by the rotary head. In this way, the drilling machine drills through the formation. More information about drilling machines, and how they operate, can be found in the above-identified references.
The feed cable system typically includes two pull up cables which couple the rotary head to the top of the tower. The two pull up cables are separately coupled to the tower, as disclosed in U.S. Pat. No. 7,413,036 and U.S. Patent Application No. 20030056993, so that the tension in the pull up cables can be different. It is desirable, however, to have the tension in the two pull up cables to be the same so that the rotary head is held level. When the tension in the two pull up cables are different, the rotary head tilts so that it is not held level.